In standard axiomatic set theory, by the principle of extensionality, two sets are equal if they have the same elements (that is, neither of them has an element not in the other). As a result, there can be only one set with no elements, hence the usage of "the empty set" rather than "an empty set".

citation

Wikipedia contributors. (2023, October 28). Empty set. In Wikipedia, The Free Encyclopedia. Retrieved October 31, 2023, from https://en.wikipedia.org/w/index.php?title=Empty_set&oldid=1182337108

Thelema (Wikipedia) Thelema (/θəˈliːmə/) is a Western esoteric and occult social or spiritual philosophy, as well as a new religious movement that was founded in the early 1900s by Aleister Crowley (1875–1947), an English writer, mystic, occultist, and ceremonial magician. Central to Thelema is the idea of discovering and following one’s True Will, a unique purpose and calling that goes beyond ordinary desires. Crowley’s system begins with The Book of the Law, a text he said was dictated to him by an entity named Aiwass. This foundational work lays out key principles, including the central axiom “Do what thou wilt shall be the whole of the Law”. This principle emphasizes personal freedom and the pursuit of one’s true path, while being guided by love and finding one’s authentic purpose.

Empty set (Wikipedia) In mathematics, the empty set is the unique set having no elements; its size or cardinality (count of elements in a set) is zero. Some axiomatic set theories ensure that the empty set exists by including an axiom of empty set, while in other theories, its existence can be deduced. Many possible properties of sets are vacuously true for the empty set.